text:
Is the vertical flight close to a building possible for GA plane?
Is the vertical flight in GA plane, so close to an actual building, as depicted in 67th second of Microsoft Flight Simulator 2020's official commercial, ever possible:

Or is there "at least a little bit of commercial fantasy" in this particular scene?
Please, note that I am not asking about law regulations, like the ability to fly with a plane through centre of Dubai etc. I am asking purely about technical aspects only. If:

nearly vertical flight,
so close a very tall building,

would ever be possible in GA plane? Or would such plane most certainly stall?

What is the significance of the building?  And what do you mean by "so close"?  Because if you acknowledge that vertical flight is possible, and aren't asking about legality, then why might the presence of a building prevent you from doing it?  Im just not sure where your root confusion comes from...

Sorry for confusion, but it seems that I am asking two questions here. One is, if such manoeuvre is possible at all. And the answer is given below (it is). For this question the significance of the building is very little. The second one is, for how long or at what height it is possible (if there are any limitations coming from i.e. gravity, height, air dense etc., not coming from i.e. limit of fuel)? Thus significance of the building is somewhat important as this is / this was the tallest building in the world and to make such manoeuvre would mean flying vertically around 1 kilometre?

But, this the side question only and the actual answer given below is far enough for me. Thank you.

Ok, well that isn't what you asked.  Your comment is clear enough, but you might want to edit your question to match.

Wayne Handley used to do exactly that in the Turbo Raven, an aerobatic monoplane modified with a Pratt & Whitney PT-6, giving the airplane a thrust to weight of more than 1.  The airplane can be seen climbing vertically in this video, but it doesn't include his hovering act, which I believe he stopped doing in the late 90s because it was quite a dangerous maneuver (an engine failure close to the ground while in the hover would probably be fatal).
I've seen his hovering act at Oshkosh in the mid 90s, and he would fly along, slowing and slowing until the nose was vertical, and he would stop in a hover in front of the crowd, literally hanging on the prop, about 200 ft in the air.  He would move the airplane in a box pattern, sideways, vertically up a couple hundred feet, sideways and vertically down, hover for a few more seconds at his starting spot, then accelerate vertically up to several thousand feet.  It was the all time most amazing airshow act I've ever seen.
The full span ailerons provided the anti-torque control, and the rudder and elevator provided provided attitude control while in the hover.  The wings are completely unloaded and are just worthless appendages, except for the anti-torque effect being provided by the ailerons.
The PT-6 version was 750 HP which will make around 3000+ lbs of thrust, and this was quite a bit more than it weighed, hence the ability to hover.  You wouldn't be able to get that power to weight ratio with a piston engine so the airplane pictured in the MFS, which appears to be a regular piston powered Extra 300 or similar, probably can't quite manage it.  Put a turboprop in it however and it certainly could, because the only limitation is the thrust to weight ratio.

The "because the only limitation is the thrust to weight ratio" is the summary and answer that I was looking for. Thank you.

The other key bit is the pilot had to master using elevator and rudder as "cyclic" control like in a helicopter, and the ailerons had to have enough surface area at the wing roots in the prop wash to generate enough roll rate to counter torque, and the very large prop that came with the PT6 provided enough "blown" air volume to make it all work.  It wouldn't work if you just put a powerful turboprop in a C-150.

Even though few civilian aircraft could sustain vertical flight, many could achieve this for a short period of time.  The main issue with a nearby building would be the exit from the manoeuvre, where collision with the building would be an obvious hazard.  A minimum of planning could avoid this though.


text:
Who is the owner of the world's only private Boeing 787 Dreamliner?
I have just stumbled across this video and I was wondering, if anyone knows who is the owner of this particular airplane (world's only private Boeing 787 Dreamliner)? I mean a man or a company -- an actual user or property owner. Not an airline / operator, because it seems to be Deer Jet.
The video itself does not reveal plane's registration or serial number, so I cannot look it up in any aviation database.
I've tried to locate it in Flightradar 24 database, based on airline / operator -- Deer Jet -- but it lists Gulfstreams and Dassault Falcons only for this operator. Neither Boeing 787 nor any other Boeing.

The registration number of this aircraft is well visible in the video: 2-DEER.
According to Planespotters, this B787 was first leased by Jet Aviation Flight Services from 2014 to 2016. During this time it was registered as N28MS.
In 2016, the plane was bought by Deer Jet, a company owned by HNA and received the registration number 2-DEER. The video was published in 2017. That means 2-DEER was not privately owned, but available and furnished for private charter clients. The video title is a tad misleading.
Deer Jet was trying to sell it for 300 million US$ in 2018 (source).
In February 2020, 2-DEER was spotted still in Deer Jet livery. It appears that they couldn't find a buyer.
The registration number starting with 2- might look unfamiliar to most of us. A company called 2-REG offers these personalised registration marks. Here is an advertising text from www.weareguernsey.com that summarizes it:

2-REG is an ICAO (International Civil Aviation Organisation) registry,
well-recognised around the world for accommodating all aircraft
categories, including commercial aircraft, business jets, helicopters,
and general aviation. In 2015, 2-REG began to issue Aircraft Operating
Certificates (AOCs), and six have been issued so far.
Run by the Dutch company SGI Aviation, 2-REG pays royalties to the
Guernsey government on operating income. The registry has built its
reputation by being extremely responsive and customer-focused,
offering its worldwide coverage coupled with competitive fees, making
it the most successful registry within the aircraft leasing sector.

I did more searches on 2-DEER Dreamliner but everything comes back to HNA China Group and no actual individual owner. Previously it was owned by Dell Technologies founder and chairman Michael Dell.
https://www.reuters.com/article/us-hna-airplane-sale-exclusive/exclusive-2-deer-chinas-hna-group-seeks-buyer-for-300-million-dream-jet-sources-idUSKCN1MZ0PM

I found this...I don't know how legitimate this is though.  It says it was owned by Roman Abramovich, but was later seized this year.
https://nypost.com/2022/06/08/inside-roman-abramovichs-ultra-luxe-787-dreamliner-jet/

A second B787 was converted to Business Jet classification at Moses Lake Washington State in US in 2018. It flew to Westover KCEF in Chicopee, Massachusetts where it has been for over a year. It is owned by Korean Air and it was for sale. It is a B787-800 N507BJ

While certainly interesting, this does not answer the original question. Please have a look at the tour to see how the site works...

Interestingly, this doesn't seem to have a tail number. At least not one painted on the plane where it's visible from this angle.

This picture was the only angle of side view that I could get.  This aircraft can be verified very easily despite this pic not having N #. The info given is factual including it is N507BJ.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
How do jetliners age (major or notable checks and part replacements)?
As commercial airliners can be (and are) operated for many years (or even decades), I've started to ponder - how do they actually age? Or - in other words - what are major or notable maintenance-related events (checks/replaces) during airliners' service life and how often do they happen?
While there are many parts that come and go every $x$ hours of flight or $n$ takeoff/landing cycles that are hard to list, my first guess was the engines or on-board computers, but then I thought about the fuselage. I assume that they are designed to withstand whole service time, but at the same time material fatigue seems to be unavoidable, and this holds for many other parts.
If that's possible, I'd especially like someone elaborated on Boeing 737NG and/or Boeing 747 (differences between the two - or lack thereof - might be especially intriguing), but any small to long range airliner will work.
If that question needs fixing/clarification, I'll be really happy to do so!

You should look up what an "A/B/C/D check" is in regards to aircraft.

On the system side, read about MSG-3 https://sassofia.com/blog/notes-on-the-evolution-of-msg-3-maintenance-steering-group-logic-3/.  Under MSG-3 most system components can be run indefinitely because they are periodically performance tested for degradation. For example, a hydraulic actuator that passes functional testing for internal/external leakage every C check (5-6 thousand hours) can run for the entire life of the airplane theoretically.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Was destruction of SR-71-related tools really extraordinary?
While reading about Lockheed SR-71 on Wikipedia I was baffled by a piece of information regarding Robert McNamara's order to destroy tools used to create Blackbirds, which took place in 1968 (at the beginning of SR-71's service), to prevent them from falling into anyone's hands.
While post-production cleanup of tools by planes manufacturers seems like a normal process (why waste space, resources, taxes, etc.), it appears that creation of any parts was impossible.
Although destruction of tools doesn't sound like a good idea to secure the technology (I somehow doubt the govt gave up on know-how and general knowledge - as for what can happen B-2's history can be a notable example), I'm still wondering:

Were all the tools indeed destroyed? If so, how were the planes maintained for all those years?
Were in said order any remarks regarding destruction of knowledge?
Why weren't the tools reconstructed after a few years?
That order sounds like a really bad idea - was there any legitimate reason for it?

Do you have any reason to doubt the 2 sources you've quoted?

Generally not, although they don't explicitly specify the extent of cleanup ordered.  So I was wondering if indeed ALL the tools and/or knowledge was really destroyed.

Think like you are a bureaucrat. No having the tools to fix an otherwise operational asset forces your hand to throw tons of money at one contractor to create a new tool or even better, a new asset. It's a win-win unless you think like a taxpayer.

was there any legitimate reason for it?
Unused tools, the tools for making a plane which isn't made anymore, are most probably put somewhere in storage, since the factory floor is best used for actual production.
While an aircraft plant for making top-notch, spyplanes is generally quite secure, any storage facility is probably less secured. Maintaining a high-security level for a storage facility seems like spending good money for a not awfully good purpose.
So in order to prevent the tools for the secret planes being stolen from a run-of-the-mill storage facility, it is much more secure to have them dismantled.
Note, that the SR-71 was produced in a time, where 24/7 surveilance was not as common as it is today. I suspect, that setting up a high-security storage facility would involve a lot of guards guarding basically junk-metal. Guarding scrap metal also doesn't seem to be an awfully motivating task for the guards.

You made me realize I assumed real ease of storing everything easily - together with @jean's comment I think it sums everything up

It's worth mentioning that 'tools' for building an aircraft are not hammers and screwdrivers. Every piece of metal probably has a wooden template around which it was cut out, and another for drilling the holes, and another to form the bends, etc. Then there are large frames for supporting sub-assemblies and even the almost complete aircraft. Even when tools are stored, it's often quicker to remake one than to find it, clean it up and fix any damage that occurred in storage.


text:
Can one fight medical rejection due to depression noted 14-15 years ago?
My husband's dream was getting his private pilot's license which he just got in August.
He was diagnosed with depression about 14 years ago and in medication less than a year. He has been great since - no depression or meds.
He did his physical this summer and got the all clear - he answered everything truthfully. Fast forward - he passed his tests and flight and has been flying since. Today in the mail he gets a letter from FAA saying his medical is rejected because he had a history of depression.

can he fight this and how?
how long is a depression bout from early 20s going to follow someone in life?

Hi Anna, and welcome to Aviation.SE. Please take the tour to learn a bit about how this site works and avoid common pitfalls like commenting via answers or answering in comments :) Good luck and I hope you stick around!

Contact Bruce Chien

I also have things in my past that wouldn't pass a Standard Issuance, and I sympathize. I would suggest to your husband something that worked very well for me: Find a local soaring club and get a Glider rating! With a private ASEL rating already, the requirements are modest. You don't need a medical - you can even have been denied a medical; you just need to self-certify that you have no condition unsafe for flight, which the past depression seems not to be. It's tons of fun, makes you a better pilot, and many touring motor gliders are just as capable as an airplane. See ssa.org to get started

There are Aviation Medical Examiners (AMEs) who specialize in special issuance medicals. It is probably best to use one of them instead of your regular AME. This type of special issuance may require a battery of psychological tests and it may get expensive. But the good news is that once he has his special issuance, he can fly under Basic Med, so he only has to jump through the hoops once.
I know of two who are regular participants on pilot message boards and they are well-respected.
Bruce Chien, MD http://www.aeromedicaldoc.com
L B Fowler Jr MD lbfjrmd@gmail.com.
Edit: I just ran across a fairly long post on Pilots of American that addresses a similar issue with a good (but time-consuming and expensive) outcome.

I wanted to share my story of a difficult SI in the hopes that it will
  give others some insight and perhaps courage to not take 'no' for an
  answer.
I had been diagnosed with mild depression during my senior year of
  high school 25 years ago. The psychiatrist I had been sent to put me
  on Zoloft (Sertraline), which I guess helped. I stayed on it via my
  family doctor for the years afterwards, not really giving it much
  thought, and never realized the difficulty it would cause in working
  towards a PPL someday. …


text:
Is everything OK with engine placement depicted in Flight Simulator poster?
Does the Airbus A320neo depicted in Microsoft Flight Simulator 2020 box cover photo has the right engine in all the wrong place?
Here is  the snapshot:

Is it only me, who clearly sees that it is way too close to plane's body and actually attached to it?
If I am correct then would that mean that someone has artificially modified the original picture, when preparing promotional photo, and made that modifications completely wrong?

Seems like a matter of perspective to me

Why are all the aircraft in the picture stalling? Looks terrible to me. (no need explaining the difference between incidence and AoA)

Turn your phone upside down, makes seeing the real position easier.

It looks OK to me:

Your confusion may come from the fact that your eyes are focusing too much on the engines themselves both of which are not directly attached to the plane but just hang under the plane.
If instead of the engines you look at the pylons you will see that they attach at roughly equal distance on both wings.

No, Microsoft's image is not doctored.  It looks very much like the image from a 2010 press release for the A320 NEO.
(Dictionaries say that doctored means deliberately altered or manipulated, in the same sense as the original question's "artificially modified".  That would apply equally well to developed photographic film, a software rendering, or even a cocktail napkin sketch.)

"Very much like", yes. "The same as"? No. So, either is has been doctored and this answer is wrong, or it's a different image and this answer is irrelevant. ;)

@AsteroidsWithWings I think Camille's point is that you get a similar optical illusion in a different (presumably undoctored) photo -- which illustrates that it's likely the plane in question has not been doctored in any way and is merely a trick of the eye. As Bergi pointed out in another answer, the lighting is inconsistent (by virtue of the different planes and background being composited together -- this is the only alteration that has occurred) which only reinforces the illusion. Note the direction of wing shadows on the yellow plane vs the A320...

"Microsoft's image is not doctored" Well, since it is a digital illustration and not a photograph, it is 100% doctored :-) That 2010 press release is also a digital illustration or rendering, rather than a photograph.

Perhaps the pedantic medium can be "the placement of the engine relative to the plane does not appear to have been doctored in this image".

The position of the engine in the model seems correct, what's wrong is the shadow rendering, causing an optical deception.
What appears to be the shadow of the engine against the fuselage (making it look very close) is actually the shadow of the wing, lighted from above.
The shadow problem is exacerbated by the inconsistent direction of lighting. The sun in the picture is in the top right corner, but the aircraft is rendered with a lighting source in the top or even front left. Look at the engine on the left wing: it's either lighted hard from the top right, in which case the engine on the right wing is completely wrong, or the shadow that we can see on the left engine is actually cast by the fuselage. Compare this against the much better rendering in @Camille's answer.

The perspective of the photo, or actually rendering, has been altered perhaps to gain a more dynamic composition.
This can be verified by looking at the nose of the plane: it seems flattened sideways, much like the nose of Boeing 737 family has. The A320 family's nose is not oval, but cirular in cross section, just a tad flattened on the top to accomondate blending into windscreens.
The shading in the rendering is not of very high quality, the fuselage section does not look right either, giving out a squarish look.
The engine location does look a bit odd, most probably due to this applied distortion, poor shading quality adds to the effect. In the model this rendering was produced from, the engine is likely in the right location.

What you're saying, then, is that they took an in game screen grab of the aircraft with the settings turned down low enough to run on my ancient computer.

Pretty much so yes

@FreeMan It seems a bit worse than that. It looks like they took a screen grab, but then rotated it in 2D. Your mind then tries to map the image into 3D space, given the cues in the image and what you know should be the 3D location for things (and the already mentioned poor lighting). This results in what feels like an oddly distorted view of the plane with portions of it a bit out of whack in your mental 3D mapping of the plane.

Why? You may ask, @Makyen... because Microsoft. :/

Very late to answer, but there is another reason :
The early 3D model design of the A320Neo for Flight Simulator had wrong proportions and component positions. As a former aircraft modeler for Flight Simulator series, side/top/front snapshots of the model and real world A320Neo comparison highlighted the differences (it's too late to produce the materials now), but :
The engines were too large and too low close to the ground. The bulge on the side was ginormous, like if the intent was to emphase the visual differences between the A320CEO and the NEO.

Why modeling errors ?
Basically, when you model a plane (or anything) in 3D, your main reference material is usually a blueprint, which is... a copy of the real thing, therefore, you're actually making a "copy" of a copy of the real thing. That's the easy way, but very prone for cascading errors, especially when the one that made the blueprint was... not that fond on doing it in the most perfect way possible. (And it's not because it comes directly from Airbus that it has to be error free - learned that the hard way).
Also, the 3D modeler may not spend 3 years fine tuning that single model; if I only have 3 months to model the thing, I wouldn't mind some "minor" (rather major) discrepancies (there will be a cockpit, the gauges, the flight enveloppe, the programming side, the testings, the optimizations, the following graphic work to have some variation... I would skip many of those, a slightly bigger engine hanging low, who would care ..?)
Thing is, when our trained eyes and brain of aviation enthusiasts look at some 3D model render of a plane, especially one that we know pretty much well, our brain will insist in tell us something is definately off... Yes, I do agree with poster, that engine isn't right (at the time. The model was fixed later - to some extent, more than once - several month after the first few batches of releases). I'm not saying that A320 is a potato model, it was actually very good, but as a matter of fact, there is a difference between "good" and "perfect" (also, there are valid reasons to not make a perfect model, but that is outside the scope of the topic)

Patchwork of virtual renders :
As someone pointed out : The Flight Simulator (ingame or debugging) rendering isn't that "perfect". Because such software have some limitation for performance reasons, optimized shading computations induces "not that realistic" renders. This further worsen the visual weirdness of the image (too clean/too much contrast/missing reflections or weathering/haze effects...)
Adding up the copy/paste of multiple aircraft from different snapshots in different lighting and perspective/field of view settings, odd nose up configuration, unnatural scene in the background, the brain had hard time to single out the A320 and resolve that - when visually isolated - it renders better and actually look alike the real thing...
No, the engine was not edited from the snapshot, just a combination of initial modeling errors and optical illusions/not well balanced patchwork.

Thank you for contributing an insider's first-hand expertise on this question!

@RalphJ : I feel ashamed to have misled you (and certainly many others). I'm not part of the Microsoft/Asobo aircraft development team. I'm just (was) part of the broad developpers community, which doesn't have formal membership, but is (implicitly) opened to everyone contributing. In such niche where a single work takes months or years, third parties contributors like me are very welcomed, especially when versed in multiple fields. You can interact and be very close to the actual developpers through the years. For a moment, I forgot that frontier, sorry for that.

No apology necessary! Your experience in building models for the simulations puts you far closer to all of this than the rest of us, and your awareness of that process, its tools, their limitations, and the shortcuts that can happen there gives you perspective that adds a lot to this thread. I understood that you weren't an Airbus insider, but that doesn't make your comments any less insightful here. We get questions based on flight simulation screenshots fairly regularly; please do stick around & contribute further.

A close look at 3-view images of the Airbus A320 neo suggests that the engine pylons are located about 1/4 to 1/3 of the distance between the first and second cone bodies on the trailing edge.  The image that you reference appears to be consistent with this for the most part.  One anomalous feature is the dark shading on the fuselage which gives the illusion that the engine nacelle is extremely close to the fuselage.  Also, compared to a similar image given in this other related answer, on the Flight Simulator image, the engine pylons appear to have possibly been shortened-- look at the relative position of the windows and the right nacelle.  But this could be an illusion caused by the fact that the aircraft on the Flight Simulator image may be banked slightly away from the observer, or the perspective may be such that the aircraft on the Flight Simulator image is slightly closer to being overhead the observer.

Perspective can be tricky in a 2-dimensional static image. It is easier to see perspective in a moving image or a simulated 3D image that you can rotate and flip. The discrepancy in the image could be due to the rendering computer’s interpretation of parallax.

authors: Vladimir F Героям слава


text:
Any aircraft that can takeoff or land on 150 m / 500 ft runway?
Just spotted on Google Maps:

What could be the purpose for building a 150 m / 500 ft runway?
I understand that no regular aircraft can takeoff or land on such distance, so certainly the reason isn't GA. In the same time, isn't this a way too long as for flying models?

Try Google translate on "club aeromodelisme".

https://arcsantcugat.com/el-video-del-arc/ , https://arcsantcugat.com/avions/ , https://arcsantcugat.com/galeries-dimatges/videos/

Interesting that no one has yet mentioned the "X"s on the runway, visible here https://arcsantcugat.com/el-video-del-arc/ .  These are relatively common features of rc runways, especially the larger ones.  On the other hand, it's a bit odd that they would paint the heading-based runway numbers on the ends of the runway (visible at same link).  I guess they just want their runway to be really, really scale-like-- not normally an objective in these situations!

@Sanchises And exactly HOW translating model airplanes club's name will bring me closer into answering my question -- if the depicted runway isn't long big as for models? Thanks for your comment, pity it is pointless.

@quietflyer Please, see my comment above. I welcome all the feedback. As long as it has any value, meaning or sense.

Steve Henry might beg to differ: https://youtu.be/zk4teJwQ6FI  (skip to 4:00 if you’re in a hurry)

Please review StackExchange rules and policies.  People asking questions are generally expected to show an effort that they tried to work the question themselves and got stuck.  Given the close resemblance between French and English on that particular phrase, at least a pass through Google Translate was called for.  Rudeness to your peers is also against the rules here.

I used to fly a Rallye Minerva that could land or take off in around 100m. I often flew from fields and strips that were being worked on. I am sure most Cubs could do that in less.

@Harper-ReinstateMonica I understand and strictly try to follow all the SO and cultural rules. I was just a little bit tired reading all comments telling me "check the club name", where in fact knowing the club name brings me even an inch closer into answering my question: "Can any GA take-off from such a short runway and if such runway isn't too long for model airplanes". I am incorrect then please, point me to any comment (not mentioning very accurate Pondlife's answer) that brings any value here or try to answer my question directly.

@copper.hat That's the answer I was looking for. Thank you for bringing an actual airplanes family name for airplanes that could possibly land or take-off at a such short distance. Maybe you could craft that comment into an answer, so I can at least upvote it. Thank you for not being another person here who thinks that translating runway owner's name is anything close into answering this question.

The club's website has some more information (emphasis mine):

Hi ha moltes coses que marquen la diferència en l’ARC però la seva
magnífica pista de 150 metres és una cosa que no deixa indiferent als
que visiten el club.
Totalment asfaltada, amb indicacions d’aproximació, carrils i ample
suficient com per aterrar el més gran dels aeromodels.

Roughly translated: "more than adequate for landing the largest model aircraft".
Some model aircraft are very large indeed (Google "giant scale RC planes"); one company's site says:

Giant Scale radio control airplanes have a minimum wingspan of eighty
inches for single-wing airplanes, and a minimum wingspan of 60 inches
for multi-wing airplanes.

It's easy to see why such a large model aircraft would need plenty of room. But there might be other reasons, even with smaller models. It would allow more people to operate at the same time, which could be important for a club with a lot of active members.
And finally, there are plenty of GA STOL aircraft that can take off and land in much less than 500'. It wouldn't allow much margin for error (especially considering the trees all around that particular runway) so it might not be safe and/or practical unless the conditions are good, but it is possible.

While we've established that this field was built for model aircraft, there are a number of piloted aircraft that can make use of a runway this short.
A general class of STOL (Short TakeOff and Landing) aircraft includes many that can, if lightly loaded or with sufficient headwind, land and take off in this distance.  Additionally, many if not most ultralights require very little runway due to their low stall speed and propellers optimized for low-speed thrust to avoid exceeding level flight speed limitations.

isn't this a way too long as for flying models

Google "pylon racer landing" -- here's a start --

  -- now imagine that happening on a hard surface-- might take some room to stop!

The club’s website seems fairly clear that it’s for model aircraft https://arcsantcugat.com/

Which doesn't say anything about if runway length isn't to long for models.

The OP asks the purpose and that is the purpose.  “I can’t land there, the runway is too long” said no pilot ever.


text:
Why do privater jets often fly at or above FL 400, but large commercial aircraft are usually in the range of FL 300 to FL 400?
With rare exceptions (like the Embraer business jet, which is simply their commercial jet with a different interior), almost all private jets fly in the more rarified air above FL 400.
But, if its more efficient, why don't airliner fly at the same sorts of altitudes on long flights?

FL360 (plus or minus a bit) is the optimal altitude for fuel efficiency, which is the top priority for airlines. And airliners all fly at roughly the same speed (again, for fuel efficiency), so ATC can just line them up in a row and let them follow each other.
The problem is that level is severely congested with all those airliners. You can’t really get out of line or pass someone, which is another reason they’re all flying the same speed—and that has become a vicious cycle because Boeing and Airbus now design their planes to be most efficient at that speed.
Business jets passengers (and thus their operators) value speed over efficiency; if they didn’t, they’d use much cheaper airline flights. However, to avoid the airliner congestion around FL360, they have to climb to FL400 or higher, where they can fly faster and likely get a more direct route.

I would question the idea that bizjet passengers value speed, and particularly airspeed, over efficiency. It's not possible to get much of an airspeed increase without going supersonic.  Most of the decrease in travel time comes from being able to fly between more convenient airports, and leave pretty much whenever you want without the hassles of ticketing & security.  But I suspect the major reasons are comfort and privacy.

The other place to operate efficiently point-to-point is the altitude largely favored by turboprops, such as the King Air or Pilatus.  They usually fly at FL 250 or so, where the only other traffic is similar planes.  As a result, even when the jetways at FL 360 are very congested, ATC will often clear a turbo to a fix just before final approach - even if that fix is hundreds of miles distant.  Turbos can be very competitve on time from (for example) NorCal to LA as you are under the jet traffic all the time.

The most interesting (and most likely the most right) is the safety issue.  An airliner with engines under the wings needs to drop to FL200 in case there is an uncontained engine failure that punctures the fuselage, requiring a descent rate of 10.000 fpm or more.
A private jet, however, has engines in the back. If an engine had an uncontained failure it would be behind the pressure bulkhead, and would not require a rapid descent due to loss of cabin pressure.
Having that - as well as turbojet engines that are low bypass and thus perform better at higher altitudes than a fanjet - makes it possible for the users to fly regularly above FL 400, where there is coincidentally less traffic as well.  And, the relatively large wing aids as well.

Not all business jets have engines in the back.  And some airliners do, e.g. the MD-80 and regional jets by Embraer and Bombardier.

Yes, I was making a genral claim to which there are exceptions.


text:
How to decide the wing span?
How would you decide the wing span for a delta wing glider?
Also how would it relate to the main chord length?

Hi and welcome to the site. This question is very likely to be closed as too broad, because it is a topic that entire books could be written about without arriving at a single solution. If you could elaborate on the requirements this wing would have to meet, it could become answerable. Also, just to be sure, are you familiar with the concept of wing aspect ratio?

Using a delta wing for a glider would not be ideal because delta wings have a lower Coefficient of lift as well as a lower aspect ratio. However you can find wing span by using the formula in the link attached: https://www.grc.nasa.gov/www/k-12/airplane/geom.html AR=s^2/A
when you use this formula you can get a idea on how well it would glide. For example the B-52 has a span of 185' and area of 4000 sq.ft., this gave a AR # of 8.56. The Concorde (Delta Wing) has a AR of 1.83 with a span of 85' and area of 3856 sq.ft. Using this formula you can determine a good AR, once you have done that you can use your numbers you have found to find the chord length by A/s=c. That should give you the chord length of your aircraft.


text:
What flaps are used for, if the aircraft has already landed?
When watching the below clip in the final approach sequence we can clearly hear setting flabs to 1, 2 and then to maximum.

At 12:05 into the clip, when fully landed plane is rolling through airport, FO says that flaps are set to 1. As I understand, they were changed from "max" to "1" a moment ago.
What is the reason of moving the flaps when plane is rolling after landing? Does it affect anything?
I am a total theoretical noob to the flying, but I was always more than sure that flaps are used to modify the lifting force of the wings (that's why they're set to "max" during final approach, to extend wings and its lift to maximum).
So, what am I missing?

They aren't used on the ground, which is why they are retracted after landing.

When I worked with LH in KUL, the A340-600 would block in with the LE slats and flaps deployed (flaps at 1st setting). I was told this was to improve cooling of the flap/slat mechanism.

@MaxR Cooling issues (31C / 86F in example clip) as outlined above in the comment (Anvil) and in the linked duplicate answer seems proving that you are wrong. There is purpose and upside of having slats extended during post-landing taxi.

A bit of ancient history:  https://aviation.stackexchange.com/questions/1189/is-it-considered-good-or-bad-practice-to-raise-the-flaps-right-after-touchdown


text:
What factors made my flight land at runway 02 in El Prat?
Aircraft normally land at Barcelona's El Prat airport using either of the 25 runways, along a flight path hugging the coast, with a flip to the 07 orientation generally associated with bad weather.
Earlier today, though, my flight landed on a cross runway, 02, which I never knew existed, with a flight path at a rather steeper angle to the coast; there is some light cloud cover but nothing to write home about. What factors drive the change to this mode of operation? I'm interested both in the general criteria and in the specific conditions tonight.
And, more generally, what are the standard resources (or types of resources) that one should use to find out this type of information?

Related

For people voting to close: there is nothing opinion based about this, as you can see from my answer.

Nor is it too broad, as there does appear to be a very specific reason.

Because 02 is the default runway for landing during nighttime (23 local time to 07 local time).

Night time configuration between 2300 and 0700 LT:
Preferential: North configuration intersecting runways
Arrivals: 02
Departures: 07R

(AIP Spain AD-2 LEBL - 8)
Airports usually have preferential runway configurations that will be used unless certain conditions (such as weather) require something else. These are usually created to avoid excessive noise to adjacent residential areas and to maximise traffic throughput.

According to the METAR history, winds at LEBL (El Prat, Spain) were from about 100 degrees until 2200Z, but they rapidly swung around to 340 by 2300Z. Still, the winds were light enough (3-5 knots) during that period that even small planes should have had no trouble continuing to use rwy 07L (3552m) or 07R (2660m); it certainly wasn't enough to prefer the shorter rwy 02 (2528m) and cut capacity by more than half--at least during the day.
If they needed to perform maintenance on either 07L or 07R, presumably the other would remain open. The capacity advantage would disappear in that case, possibly favoring 02 for the winds, but not the length advantage.
My hunch is that local noise abatement procedures dictate arriving aircraft avoid flying along the coast at night, when presumably traffic levels are low enough to allow intersecting-runway operations, whereas noise sensitivity is lower during the day despite traffic being higher.


text:
Do negligible weights affect the control of a commercial aircraft?
I was watching a video and it said that switching seats on a commercial airplane would be fatal. "Switching of seats from the rear of the airplane to the front seats would result in probable accident". I think if a person weighing between 40-110kgs would be considered as of negligible weight relatively to the aircraft weight.
Do such acts by passengers really affect the controls?
Reference:

A little bit of knowledge is a dangerous thing.  The short answer, based on the definition of "negligible", is no.

Welcome to aviation.SE.  One useful tip is to do a quick search before you post a question.  I clicked the tag you included (weight-and-balance) and not surprisingly found that several of the first 30 questions were asking basically the same thing.

By the definition of the word "negligible," negligible weights don't have any significant effect at all. When you wrote "negligible," did you mean to write "very small"?


text:
How do Flight Test Engineers plan and execute sortie profiles?
Can someone from the field explain with a simple example the process of planning and executing a sortie profile as an FTE. Any reference books for an insight into the subject would be appreciated.

Three main factors influence the flow of a flight test sortie: data requirements, test point priority and flight efficiency.  For example, consider a test sortie that requires evaluation of stall handling qualities.

Data requirements specify which altitude, weight and cg, and configuration are required for each stall test point, for example.
Test point priority comes from the test team or test plan. One test point may be more important than others.
Flight efficiency refers to the need to minimize time between test points, minimize wasted fuel, and consider geographic position or airspace boundaries that may affect the test.

Balancing all of these things requires experience and judgment.  At the beginning of the flight, the aircraft is heaviest, so it makes sense to do test points that require heavy weight.  The second most important thing is to consider high priority test points. What points of high priority combined with heavy weight should be considered.  Finally, deciding the flight path that accommodates these two characteristics is the last factor.
This combination of judgment and knowledge and skill is difficult to describe accurately, and often two experienced professionals will come up with different, and equally acceptable, answers.

EASA has a general guideline on the topic here

The FAA provides guidance by a/c type. AC 23-8C - Flight Test Guide for Certification of Part 23 Airplanes, AC 25-7D - Flight Test Guide for Certification of Transport Category Airplanes, and AC 90-89B - Amateur-Built Aircraft Flight Testing Handbook


text:
is there difference b/w moving object in a fluid and static object in a moving fluid?
wind tunnel is usually based on static object in a moving fluid, but wouldn't stationary/semi wind inevitably fill the tunnel after collision, but in the real world the moving object is always meeting a new particle and the previous ones always leave the field.
if indeed there is an actual difference wouldn't that render turbulence simulation impossible?, and also incorrect CFD simulations?.
since wind tunnel do exist there can't be any difference but why?

if fluid is moving in a large tube and you put a box in it's center would you expect it's back to be vacuum forever, b/c any fluid that goes behind the box wouldn't leave. but normally if an object is moving at a high speed depending on it's shape there should a  vacuum at it's rear.

That's called Galilean invariance. There's no difference whatsoever between a steadily moving object in a stationary fluid, and a stationary object in a steadily moving fluid.
You seem to be thinking that in a wind tunnel, some air will always get trapped downstream of (that is, behind) the object; and that for an object flying outdoors, air will never get trapped behind (that is, downstream of) the object. Neither of those things is true.
I see that you're thinking about supersonic flight; you're saying that

it seems like if an object is flying supersonically, it will leave a vacuum in its wake, but
it also seems like if an object is stationary in a supersonic wind tunnel, it will not have a vacuum in its wake.

I actually agree with your intuition here; I also think it seems like these two things will happen.
But when my intuition contradicts a law of physics, it doesn't mean that the law of physics is wrong; it means that my intuition is wrong.

not to be rude but i understand your still puzzled by it but given up. hopefully my intuition will be back on track soon, wouldn't wanna argue with myself every time i remember it.


text:
What is "Boost"/"Super Boost" in the PW127M/N?
This incident describes rejected take-off due to the "boost" being inoperable. The reason for the RTO is obvious: engine power lower than expected.
But what is this ominous "boost" technology?

The boost function has nothing to do with the ATPCS. All ATR variants have ATPCS. It allows for take-off with reduced power, which increases engine life.
The PW127M has a "Boost" function that allows for a higher turbine temperature (ITT) at take-off when the power is temperature limited. Boost is selected ON before take-off when required. Typically, it allows for 500 kg extra payload. However, this comes at a cost: Every time boost is used, engine life is reduced.
The PW127N was specifically developed for Avianca in Colombia. They operate out of Bogota, which has an elevation of 8,700 ft. The PW127N engine has a "Super Boost" function that allows for an even higher ITT at take-off. This increases the payload by another 500 kg or so.

Welcome to aviation.SE! If you can add some references for this answer, that would be great.

Looks to be an interesting document here: https://www.scribd.com/document/426439514/Boost-Option, but scribd only makes the first page available for free.

The boost function "cool down" the engine when needed, and adds 4.5% power below 4000 ft, 4% power above 4000 ft and 4% power when at MCT (maximum continuous thrust)

The mentioned atpcs is a system that provides the aircraft with an increment of 10% of the total power at take take off in case of engine flame out, the power rating in normal take off has a maximum of 90% torque, if it's not limited by temp, that's 2475 shp, with the rto (reserved take off power) it's 2750 shp, that means when you take off and a flame out occurs the atps automatically add 10% power to the remaining engine and the affected engine autofeathers it self (when arming on ground)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Has anyone compiled all the NTSB accident reports and broke down the percentages for cause of accident and fatalities?
I am not talking the typical breakdown such as Pilot/Mechanical/Other, but rather, more specific things such as, engine failure, Stall/Spin on approach, controlled flight into terrain... etc

The closest thing I can think of is the Nall report - I'm not sure if that's the level of granularity you're looking for though...

@raptortech97 I think you are looking for avherald.com but that doesn't include all reports for various reasons

@voretaq7 - This is great information about the conditions and type of flight, but I still don't see the cause on there anywhere.

Out of interest what do you want the information for?

I am an engineer/entrepreneur, and I'm hoping to create my own airplane company. I am doing initial research into the feasibility of making an electric (possibly VTOL) LSA which compensates for most pilot mistakes with an end goal of making a GA plane flight safer than a car ride.

@David It already is.

@HCBPshenanigans - Unfortunately, this is not the case for GA aircraft, only commercial. The safest GA plane by record is the Diamond DA40 (with the popular C172 close behind). It has a fatality rate of 0.35/100,000 hours flown. For Driving, the statistic is around .588 fatalities per million hours driven. Even taking into account miles traveled, the safest plane was still at least 4x times the risk in a best case scenario.

@David - I suspect the hard part of designing an LSA which compensates for pilot mistakes won't be when the pilot tries to do the right thing and fails, it will be compensating for when the pilot tries to do the wrong thing, and succeeds.

@SteveV. - I agree. Most accidents are a series of thoughtless mistakes which is the true tragedy. Making GA safe from this is the first step to truly safe, near automated flight.

Have you seen https://aviation-safety.net/ ?

@AnthonyX - Yes, I have, but I don't believe they break it out by cause on a large scale basis but still a great site. Let me know if I'm wrong.

2 big causes are VFR flight into IMC, and running out of fuel.  Since you're suggesting VTOL, create a system that can auto-land when IMC is encountered (autodetect weather? pilot hits panic button) maybe allow the pilot to take control back when VMC is encountered again), and auto-land when there's still sufficient fuel/battery charge TO land (i.e. don't let the plane run out). And put it on floats in case the landing is over water.    I think you can only take so much danger out of flying before you take the utility out of flying tho.

There's a book called "The Killing Zone - How and Why Pilots Die" by Paul A. Craig which has a great deal of statistical work in it around aircraft accidents which may be useful to you. It's an alarming title which might make you think it's some sort of sky is falling mentality, but it's actually very sensible, statistics-based information about aviation accidents.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Besides size, what determines the cost of creating a composite structure for a single engine piston aircraft?
When designing an aircraft (LSA or GA), how would one minimize the cost of construction when the aircraft is composite. To be clear, I am talking only about the structural components, not the interior, engine, or instruments.

this seems an engineering.se question, rather than an aviation one.

Apologies guy, not attempting to drift off topic with my questions as I thought this was acceptable in this SE. I am not sure who has privileges to do this, but I personally would like general aviation engineering questions to be either explicitly on or off topic in this SE as I would not really say this is clear at http://aviation.stackexchange.com/help/on-topic. As home building is an activity that many aviation enthusiast take part it, I'd prefer it be on topic.

Cost drivers for composite structures:

Weight: Lighter is harder to do and needs more work and more expensive materials.
Surface quality: Either you use lots of filler and several sanding and filling cycles, or you produce a high-quality negative mold, which is a lot of work.
Reproducibility: If you want to produce several identical parts, you need to produce a reusable negative mold. Simple composite structures can be built in a positive technique.

Positive building techniques
You can either use a styrofoam core which you cover with fibers and epoxy (just as Burt Rutan did), or you build a balsa wood core on a simple jig and cover it in fibers and epoxy on both sides to produce a sandwich shell. In both cases you build from the inside out and have to finish the surface with repeated cycles of filling and sanding until you arrive at the desired contour and surface quality. This is a lot of work already, but much simpler than building a negative mold.
Negative building techniques
Here you first produce a core of the desired shape (again much like the styrofoam-epoxy structure above) and use this to produce two casts which will serve as the mold in which to build the eventual structure, or you take a large CNC mill and have it produce the mold from a big block of aluminium (or another suitable material). Now you will build the structure from the outside in, so you achieve the desired surface quality without filling and sanding the final structure, and you can repeat this process to produce several identical pieces until the mold is worn out.
If you add up the material and labor cost of the two techniques, you will find large cost differences which are reflected in the quality of the final parts.

Hey Peter, Thanks for all the fantastic answers! I couldn't help but notice that you are the correct answer on most my questions? Would you mind if I ask what your background is?

@David Aerospace engineer with a PPL.


text:
Pointers to Aviation Scholarships
I want to become a pilot, but as you know, I should take some training course on aviation. Currently I am searching for Aviation Scholarships because I can not sponsor myself. Can you give me some pointers please?

This question appears to be off-topic because it is about finding funding to learn to fly.

Scholarships dot com has a list of a few scholarship programs:  https://www.scholarships.com/financial-aid/college-scholarships/scholarships-by-type/aviation-scholarships/
However I am not sure if you are looking to get aviation training for a career, or for personal fulfilment.  There are also some schools that offer various aviation related programs (Embry-Riddle being the best known in the US).  Some of them may have separate scholarship programs that are not specifically listed on the Scholarships.com site.
There are also some places throughout the world that offer "learn to fly" programs.  I have a friend that works for a company that even offers their employees all the coursework and flying required for a private pilot license as a training subsidy (Kollsman, in New Hampshire).

Thank you. I look to get aviation training for a career.

What country are you located in?  The scholarships link I provided are mostly for the US.  If you are outside the US, I don't know if those would apply.

I am in Ethiopia, Africa.

Maybe this will help: http://blog.internationalstudent.com/2012/10/aviation-scholarships/

And here is a school in your country.  They may be able to offer some advice on a scholarship: http://www.ethiopianairlines.com/en/schools/pilot/


text:
How would exhaust heat recovery into the combustion chamber affect the efficiency of a jet engine?
So, a jet engine basically sucks in air, heats it up and spits it out, right?
The hotter the air gets, the faster the exhaust velocity and thus the more efficient (Higher specific impulse).
Now my question is how this all gets affected if you use a heat recovery system, either a heat pump or a simple heat exchanger. Let's ignore the annoying practicalities of metals melting and all that stuff and just look at the theoretical side.
If you recover heat from the exhaust and put it back into the combustion chamber how does this affect the efficiency of the engine? If we were to apply the heat into the combustion chamber using a heat pump, pumping heat from the exhaust into the chamber could we get even higher efficiencies? While "Yes/No" answers would suffice I would be much more interested in a thermodynamic explanation and possibly even some estimations of the theoretical efficiency which could be reached using the Carnot cycle for pumping the heat.
Onto the practical, has anything like this been experimented with? To my knowledge we don't have heat pumps capable of operating at 2000 degrees Celsius and pumping heat quickly enough to compare to any type of engine, but maybe someone has experimented with simple heat exchangers like how rocket engines use regenerative cooling (for different purposes though, but still similar to this).

What efficiency are you implying, fuel efficiency or thermodynamic and/or propulsion efficiency? Heat recovery is very beneficial for the fuel efficiency!

You would probably make the engine too heavy to fly.  Heat recovery is used in gas turbine electric generators (which are basically jet engines).  Here's what the equipment looks like: https://en.wikipedia.org/wiki/Heat_recovery_steam_generator

A thought exercise suggests that if you measure difference in the energy within the air before the vehicle does through versus then after, you are emitting more energy if the difference is higher.  In internal combustion or power generation you want a suction on the back of the turbine because the thrust is transported to a generator.  In a jet you are getting thrust from momentum transfer.  Kinetic theory of heat says higher mean momentum of gas is higher temperature.  Also, heat transfer requires a temperature difference, and Le Chatelier's principle is a harsh mistress.

Extracting heat from the exhaust will cool and compress it, slowing it down and reducing thrust. Recirculating the heat back into or downstream of combustion will raise the temperature at that point and on downstream to the extraction point. The inevitable thermodynamic losses mean that the returned heat does not quite compensate for the heat drawn out and overall efficiency will fall a little.
What does improve efficiency is to draw through additional air mass in order to increase the exhaust mass flow, even at the expense of lower overall velocity and temperature. This is what the bypass turbofan does.
A more radical modification is to swap the combustion chamber for a heat exchanger and heat the gas via hot fluid from an external source; the hotter the fluid the better. I have seen this proposed for the hydrogen turbopump in some versions at least of the SABRE air-breathing rocket engine. It was also proposed for nuclear-powered bombers in the 1950s, though I cannot recall if those included turbojets as well as ramjets.

A couple of remarks:

The reaction jet engine produces thrust in the exhaust nozzle. In a subsonic engine the exhaust gas first accelerates in the convergent section of the nozzle then it expands in the divergent section. Expanding, the gas looses not only kinetic energy but it cools down as well. Since the thrust is developed in the last section of the nozzle then having a heat exchanger further down would actually reduce the thrust by reducing the ability of the gas to expand.
There is a reactive jet engine that uses heat exchanger. Is called Sabre and the developer tried to solve the problem of suborbital flight using one engine only. At takeoff the engine functions as a reaction jet. Once the speed exceeds the range of usability of the axial compressor, then a heat exchanger placed in the air intake cools down the air to maintain the efficiency of the axial compressor even at supersonic speeds. The airflow through the engine remains subsonic. However, on exhaust the afterburner provides the extra thrust required to maintain speeds in the vicinity of Mach5 to 7. This engine burns hydrogen and uses liquid helium as coolant, or so the developer says. This is a bold undertaking from a private developer.
To answer your question: The Sabre is an example of using a heat exchanger in the air intake. The only cooling in the exhaust is meant to keep the hot side operational and not to extract energy from exhaust gas because that will affect the thrust.

I might quibble with 1. a little bit.  I would say the reaction is generated along the entire path from the burner can outlet aft, but mostly between the turbine and nozzle as the flow is forced to accelerate by the convergence.  Also non-afterburning engines don't have a divergent nozzle section. It narrows down to the nozzle outlet and that's it.  The "divergent" part is just open space.  The divergent nozzle section is only present on an afterburner nozzle and only while in reheat.

The reactive force in the reaction jet happens in two places only: in the axial compressor and in the divergent stage of the exhaust nozzle. The turbofan takes advantage of compressor thrust by employing fan stages. The exhaust nozzle is formed by a fixed diffuser cone at the interior and an adjustable shell at exterior. Even when the adjustable shell is fully closed it still forms a ring shaped divergent nozzle. Usually the nozzle convergent side is missing because the turbine extracts work from exhaust gas hence recompressing the gas after the turbine would decrease efficiency.

So basically, any attempt at recovering heat would result in a decreased expansion and thus decreased  thrust and efficiency?

If you cool the exhaust gas, the speed decreases (speed depends on temperature) and the flow vein contracts; it gets denser and slower. Won’t exert more pressure on the walls of the divergent nozzle (in fact the pressure will decrease because of contraction), therefore less thrust will be achieved. However, if you cooled the intake air, then denser air entered the compressor. The air will then be compressed and heated the same, but starting from a lower temperature the final state will result in higher pressure.

Am I reading this correctly? The heat exchanger is cooling the intake air, right? That would make sense, since you want the intake air as dense as possible.

@Dean F. Yes, that's how it works.

Theoretically, in an infinitely efficient system, there would be no net difference. The energy lost in the exhaust would be added back to the combustion chamber to be lost again in the exhaust. Maybe, you could use this heat exchange side engine to run another system without losing engine power. But, there is never something for nothing. Although I've read that the cowled radiator for the piston engine spitfire did produce a small amount of thrust as a biproduct.
This is all predicated by the fact that the heat energy is dumped back into the whole system in or after the combustion chamber. If it's before the the compressors, it would lower the density of the air coming in. Your thrust is based on the mass of the air being accelerated. If it dumped into the compressors, that energy may be lost to the peak amount that the compressors can increase density and pressure. It would be lost in the current way compressors shed excess heat. If the compressors could be made of material that did not need to be protected from excess heat, then there would be no need for the heat exchanger adding heat. It would already be there as a biproduct of compression. Therefore, you would not need to rob it from the exhaust.

The "Meredith" system used in the Spitfire radiators was just an embryonic thermal ramjet: gas channelled through an asymmetric duct and heated in the middle.

Efficiency of the combustion zone is greater if the compressor delivers cooler air. Turbocharged piston engines sometimes have an intercooler stage after initial compression.


text:
ETOPS between Johannesburg, South Africa, and Perth, Australia
South African Airways flies over 6 000km across the Indian Ocean from Johannesburg, South Africa, to Perth in Australia.
I don't see any airports along the way in the event they need to divert.
Does anyone know what would happen in an emergency?
PS Yes, yes, I know that ETOPS does NOT mean "Engines Turn Or Passengers Swim"!

ETOPS originally was an acronym for Extended Twin Operations. While it has been changed to just Extended Operations, the focus is still on twin engine aircraft. South African Airways currently operates the route with an A340-300, which has four engines. If it has an engine failure, it is not as much of an emergency as in a twin-engine aircraft, so it does not necessarily have to adhere to the same ETOPS rules for alternates.
Johannesburg to Perth is certainly a fairly remote route. But at least eastbound it's less than 10 hours, and, for example, the A350 is certified for 370 minute ETOPS. This is 6 hours, and while that is at a one-engine cruise speed, it's still fairly close to covering the entire route.
Looking at the Great Circle Mapper, a 240 minute ETOPS would be enough to fly the route with only a slight diversion from being direct. This is with 300kt diversion groundspeed. From the map, it appears that Mauritius and Cocos Island could serve as alternate towards the middle.


text:
How to remove a course reversal (hold) on a Garmin 530W?
How can I remove a course reversal, (hold) from the FLP page on an RNAV approach ?  If I want to do a straight in (NoPT) it will not allow me to remove the hold without removing the whole waypoint.

When loading a straight in approach into a GNS430/530, once you select the airport, approach and IAF, then hit ENT to either load approach or load the approach and activate, it will bring up a dialogue which asks if you want to fly a course reversal at the IAF.  If you select no, then no hold will be placed in the flight plan.  If you have entered the course reversal at the IAF for a straight in approach, you can still remove it by opening the FPL page, highlight the hold and press CLR to remove it.  It will ask you if you want to remove the course reversal one final time.  Select yes and press ENT.


text:
Constant turn radius with Δ airspeed and bank
Can someone explain how speed impacts rate of turn and and degree of bank required?
I'm trying to understand this practice problem but can't get the concept: Say you have 2 vehicles travelling at different speeds and carrying out a turn at the same radius. The example states that the faster vehicle will have to bank at a shallower angle and will have a lower rate of turn.
In my mind, the faster vehicle would have to maintain a steeper bank angle to compensate for the higher relative speed, otherwise their radius would increase. If you're moving faster, and banking at a lower angle, wouldn't that mean you're travelling at greater forward distance and less lateral distance thus increasing you're radius?

I am with you on this question.  The faster the object is moving the faster the rate of change will be around the turn.  The rate of change of direction has an affect on the centrifugal forces (forces pushing away from axis of rotation).  The goal in an aircraft turn is to have the centrifugal and gravity forces being equal resulting in a coordinated turn.

You are right on all accounts.
In a steady-state turn, from circular motion, we have, with $F_c$ being centripetal force, $V$ being airspeed in zero wind, $R$ being the radius of turn, and $m$ being the aircraft mass:
$$F_c=m\frac{V^2}{R}$$
The centripetal acceleration in a coordinated turn is created from the banked lift vector ($L$), therefore, with $\phi$ being the bank angle:
$$L\sin\phi=m\frac{V^2}{R}$$
Therefore, the radius of turn is:
$$R=\frac{V^2}{g\tan\phi}$$
and the rate of turn is:
$$\dot{\psi}=\frac{g\tan\phi}{V}$$
As speed increases, you would need an ever larger bank angle in order to achieve the same rate of turn. Of course, there's a limit to how much lift you can get out of the wing at a given speed, especially at higher Mach when transonic buffet becomes the limiting factor.


text:
What is the beeping occasionally heard in the background of ATC?
Occasionally while listening to ATC, I hear a beeping in the background of their transmission. My suspicion is it's a traffic conflict alert since the beeping is usually followed with a traffic alert to a pilot. But other times I've heard the beeping without a traffic alert.
Here is a short snippet from today of Norcal Approach at KOAK demonstrating the beeping heard in the background: https://vocaroo.com/lD93L8D5lJ3

I can't identify the specific sound, but - just like in a cockpit - there are several different audible alerts in a control tower/control centre. Just to list a few:

Conflict alert, as suggested in the comments
Various other radar based safety nets (MSAW, MTCD, DUPE etc.)
Strip printer printing a strip (not an alert as such, but the sound is quite noticable)
Phone ringing (typically a tower has several different phones, possibly with different ringers)
Fault indication on a runway light/navigation aid
Change in status (on/off) of ILS equipment (localiser, glideslope, DME)
Crash alarm, when activated by the controller
Microwave/toaster timer! (at least in smaller towers without a separate kitchen or break room)
Several others, depending on the local equipment

It may be a bit startling when you hear something on the radio that sounds like some sort of alarm, but you shouldn't be worried. The sound can signify many different things and it does not necessarily indicate anything dangerous.

Anecdotal comment: The first time I used our toaster at work it almost scared my to death with an extremely loud beeping as the timer ran out.

Makes me think of the Pop Tart scene in Pulp Fiction :)

To me that definitely sounds like STARS' initial CA aural alarm. My thinking is strengthened by the traffic call (eleven o'clock, mile and a half). The "oh shoot" alarm has the same tone but faster.

It could be a traffic alert (or low altitude alert, or 7700) on a different sector. Many controllers sit in a room together at neighboring scopes; I've occasionally heard a couple of seconds of conversation and other background noises.


text:
What are some common factors that affect GA aircraft manufacturability?
Recently, we've seen Icon go through layoffs due to production delays related to "Manufacturability". I assume this is due to their wing structure in part, but I'm curious, in general, how a company goes about designing with manufacturability in mind.

this seems an engineering.se question, rather than an aviation one.

I think it's definitely aviation but rather broad.

Apologies guy, not attempting to drift off topic with my questions as I thought this was acceptable in this SE. I am not sure who has privileges to do this, but I personally would like general aviation engineering questions to be either explicitly on or off topic in this SE as I would not really say this is clear at http://aviation.stackexchange.com/help/on-topic. As home building is an activity that many aviation enthusiast take part it, I'd prefer it be on topic.

This answer can only scratch the surface - a good answer would take you several days to read.
Manufacturability is the combination of several things which combine to

improve the repeatability of the finished products without much individual reworking, and
reduce the work hours required to produce a given component or system

under the local conditions (wage level, worker skills, energy prices, logistics etc.). This list of factors is incomplete but should give you an idea what is involved.
This is done by selecting the proper techniques (lots of jigs and molds for repeatability, the fewest amounts of parts and joints for reducing man hours) and by designing the system such that producing the components and combining them into the finished product can be done quickly and with the available workforce.
An example: When Fairchild joined up with Dornier, they planned to relocate the production of the Do-328 from Bavaria to Arizona. The production line in Germany was set up for the local workforce, and since they were highly skilled metal workers, the holes they drilled manually were straight within ±2°. In the USA, however, Fairchild could not find enough adequately trained workers, so the production line would had needed jigs for every single hand-drilled hole - and there were lots of them on the 328. The whole endeavor floundered because the production line was not designed for manufacturability under the new local conditions, and remedying this would had cost too much.
Another example would be the Tu-4. This was a Russian copy of the Boeing B-29, which the Russians had ample time to study after some landed in Eastern Siberia after attacks on Japan. But it was no cheap knock-off: The Tupolev design bureau redid the design, airframe, engines, systems and all, in metric dimensions, so standard Russian gage sizes, fasteners and tools could be used. It was re-designed for manufacturing, in other words.


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What is the current state of regulation regarding VTOL aircraft in the LSA category?
With quite a few concept designs in progress, I am curious what the current FAA regulations are regarding vertical takeoff and landing vehicles in the light sport aircraft category.

Interesting question, do you have any links? The current definition of LSA excludes helicopters and powered-lift, so any VTOL design would have to avoid being classified as either of them.

Not sure that I have anything too reputable. I saw a sketchy manufacturer "concept" vehicle mention the two in the same sentence which is why I asked.

The FAA term for VTOL [other than helicopters and lighter-than-air craft] is "Powered Lift". Also of note, gyroplanes by nature may be able to land vertical but cannot takeoff vertical so are not VTOL.
LSA excludes powered lift. Not much more to it, unless maybe it launches from a catapult and lands with a parachute.
title 14 CFR section 1.1 "General definitions":

Light-sport aircraft means an aircraft, other than a helicopter or
  powered-lift that, since its original certification, has continued to
  meet the following:
(1) A maximum takeoff weight of not more than—
(i) 1,320 pounds (600 kilograms) for aircraft not intended for
  operation on water; or
(ii) 1,430 pounds (650 kilograms) for an aircraft intended for
  operation on water.
(2) A maximum airspeed in level flight with maximum continuous power
  (VH) of not more than 120 knots CAS under standard atmospheric
  conditions at sea level.
(3) A maximum never-exceed speed (VNE) of not more than 120 knots CAS
  for a glider.
(4) A maximum stalling speed or minimum steady flight speed without
  the use of lift-enhancing devices (VS1) of not more than 45 knots CAS
  at the aircraft's maximum certificated takeoff weight and most
  critical center of gravity.
(5) A maximum seating capacity of no more than two persons, including
  the pilot.
(6) A single, reciprocating engine, if powered.
(7) A fixed or ground-adjustable propeller if a powered aircraft other
  than a powered glider.
(8) A fixed or feathering propeller system if a powered glider.
(9) A fixed-pitch, semi-rigid, teetering, two-blade rotor system, if a
  gyroplane.
(10) A nonpressurized cabin, if equipped with a cabin.
(11) Fixed landing gear, except for an aircraft intended for operation
  on water or a glider.
(12) Fixed or retractable landing gear, or a hull, for an aircraft
  intended for operation on water.
(13) Fixed or retractable landing gear for a glider.

A link to the appropriate FAA document would greatly enhance this answer.

@AEhere There it is, title 14 section 1.1

Well, it looks like a (sufficiently-small, single-engine, no-more-than-two-seats, unpressurised) airship could potentially meet all of those requirements...

A few gyros, fitted with collective-control rotors, can perform no-roll, vertical (or almost vertical) takeoffs. An example is the A&S 18A: https://www.youtube.com/watch?v=wzAcNh56B5A

authors: Константин Тычинин


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Are there any future regulations planned for electric multi-motor LSAs?
It seems with electric control of the multi engine configuration, such as with NASA's new leap tech technology, that there should be a way to use multiple motors in the LSA category. Is there anything in the works regarding regulations for this type of aircraft in the LSA category?

Last I read, the FAA hadn't made provision for manned electric aircraft of any type. It's possible that multi-rotor electric designs would constitute a new class (or even multiple new classes) of aircraft. It's probable that such a concept will (or won't) be proven in the experimental aircraft community. If it represents a viable model for commercial development, external pressure would force the FAA to acknowledge, and regulate it.

At least in the US, LSA certification is the purview of ASTM F37. They don't seem to have a subcommittee dedicated to multi-motor anything, and I didn't dig deeply enough to see whether the existing committee has any standards for single-engine electric LSAs.

As for Europe, currently the issue is not considered. Currently multi engine configurations do have certification advantages as an engine failure is not seen as critical as for single/double engine configurations.

Light-Sport is a category for pilot certification and flight rules. The aircraft themselves are simply part 23 normal category risk classification level one, low speed.
Part 23 was fully rewritten in 2016 it now describes the desired safety outcome but lets manufacturers develop new methods of complying, nothing is bias against electric multi-motor planes in the new part 23.
The issue is that the pilot must be rated for multi-engine operation and you must have at least a private pilot certificate for the multi-engine rating. Most multi engine training is actually about operating with an engine failure and the associated aerodynamics.

Can you edit your response and provide a link to the new Part 23 rules? Can you provide an article that asserts the same opinion you've expressed here about the new rules?


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What is the easiest way for a new private pilot to visit Manhattan?
As a goal, I would like to:

Limit the difficulty of the class B airspace by staying at uncrowded areas
Minimize the time it takes to get into the city

All of NYC's airspace is crowded, so there's no escaping that! :) The controllers are very friendly and accommodating though, so don't be afraid. If they're curt, it's just to keep everyone safe. As for airports, there are 4 GA airport options you're most likely gonna consider:

KLDJ in Linden, NJ. It's a 5m cab ride to the train station into the city. Uncontrolled field, tons of news helicopters based here. It's pretty cheap (around $20/night if I recall) and fairly convenient, but the uncontrolled field is under an 800' Class B shelf at Newark and could be stressful. Expect very bare bones facilities - you can get fuel, but there's no terminal building to speak of.
KTEB in Teterboro, NJ is the GA airport for most jets that come into the city. It's the closest airport to midtown, and you'll pay a very pretty penny here, tie-downs are at least \$50/night, and fuel will be around \$9/gallon. This is a hectic option, but it has a tower and is close to the city, so for a quick overnight stop without fuel it may be the best option. Expect to be the only piston on the ramp.
KFRG in Farmingdale, NY (Long Island). Very busy GA airport abuzz with training. Pretty cheap (~$15/night tiedowns), but did I mention that it's busy? You may burn up 1h of hobbes time on the ground waiting to take off if you depart during peak times. You can catch a cab to LIRR which will get you into the city.
KHPN, in White Plains, NY. Mix of GA, training, and a couple commercial carriers like JetBlue. Prety cheap ($~20/night tiedowns) and a short hop away from Metro-North which will have you in the city in about 30 minutes. Controlled field, at 2500' below the Class B shelf. Fairly busy, but certainly managable with the top notch controllers working NY's airspace.

Whichever airport you choose to go to, absolutely get flight following or file IFR. All of the towers in the area expect you to be handed off from NY Approach and will not be happy if you call them directly out of the blue.

Just curious - how accurate is this, 9 years later?


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How is it possible that the design criteria for turbulence intensity has nearly doubled, but the manoeuvring load factor is the same?
https://www.law.cornell.edu/cfr/text/14/25.341
Here it says the turbulence intensity used for certification is 90 feet per second. Before, it was 50 feet per second, that section was added in 1981. So since 1981 the criteria has almost doubled.
But how is it possible that the maximum manoeuvring load factor has remained exactly the same? A transport category plane designed after 1981 still can't pull a nearly 8 G turn.

Isn't the turbulence intensity actually expressed as acceleration in fps²? 90 fps² calculates to 2.79G. Earth's gravity acceleration at sea level is about 32 fps².

No, it's the speed of the 'gusts' (or more accurately, the sharp whirlwinds) that make up the turbulence. A transport plane encountering a 50 fps+ intensity patch of atmospheric turbulence at cruise speed would likely experience accelerations of around 3+ G, or 'extreme turbulence'.

Does this answer your question? What kind of weather conditions would produce turbulence with an intensity of 90 feet per second?

In that case this question is a duplicate of https://aviation.stackexchange.com/questions/87868/what-kind-of-weather-conditions-would-produce-turbulence-with-an-intensity-of-90?rq=1.

It doesn't address why the aircraft could theoretically handle (for example, 7-8+ G) worth of bumping and shaking, but not 7 or 8 G in a turn or loop. In transport aircraft designed prior to 1981, the discrepancy was narrower, ie; a passenger aircraft will break if it does a 4 G turn, and will break if it encounters turbulence in the range of 4-5 G.

This question also addresses your query. https://aviation.stackexchange.com/questions/83458/what-is-the-maximum-momentary-g-force-that-a-modern-airliners-wing-can-take-bef
The 90 fpm limit is for momentary force, not sustained force in a turn. Boeing tested their 787 wings by bending them until the tips touched, and they did not break.

My question boils down to; how is it possible for an aircraft to withstand very high momentary forces, but not very high sustained forces?

@JuanJimenez, no, the turbulence intensity is expressed as velocity difference in the wind shear. There is inherent acceleration involved in the turbulence itself, acceleration is only caused by the sudden change of the flow conditions around the aircraft and thus the resultant aerodynamic forces.

@ItisTiff_93 it isn't about momentary and sustained forces (that much; flexing smooths the spikes a bit, which helps), but rather about how big aerodynamic forces a sudden wind shear can generate.

@JanHudec you should answer.  The concept is the same as a shock absorber/spring smoothing bumps in the road by flexing (with flexing can cause metal fatigue in mind).  So the design criteria could include long and short term loads in any direction (with flutter/resonant frequencies in mind)?

@JuanJimenez I don't believe any aircraft ever has been tested and shown to handle wing bending until the wingtips touch. Care to cite a source, I'm certain this is an urban legend? The wings of modern airliner do withstand bending wingtips way above the top of fuselage.

@jpe61 Sure they touched, just not themselves. :)

This question was posted twice on Reddit

Turbulence intensity applies to the air around the aircraft.
The sustained load factor applies to the aircraft itself.
These are apples and oranges, one cannot be directly compared to the other.
In a simple model of a high-G turn, the air remains stationary, and the aircraft increases its lift N times. Thus its wings have to be designed to carry a load of N*W (with fatigue and safety factors).
Gusts or turbulence also produce forces on the wing. But not as much force as would be required to impart the same amount of acceleration to the aircraft as the apparent acceleration of air in the gust. A fan that blows at X fps doesn't make every object in the room move at X fps.
A gust of 90 fps across a stationary flat plate would impart about 12 lb/sqft of pressure. A modern airliner's wing loading is between 100 and 140 lb/sqft. Real numbers will differ a lot, because it's not a static case at all, and manifests as an AoA change, with increased/decreased lift.
Still, it's not extra G's of force, as that would require far more velocity.
What makes turbulence dangerous and very perceptible is the rate of change in acceleration, called jerk, not absolute acceleration. Its erratic behavior also contributes to vibration and fatigue. The added force is only a fraction of what the wing normally carries, but its rapid onset and cycling can be dangerous.
Increased design turbulence intensity is a requirement to account for these secondary factors, not to build more static strength into the design.

A 90 fps is also ~45 knots, which, when combined with the forward speed, means quite significant change in angle of attack. But that's what the weather penetration speed is about—if the wing stalls before overloading, it isn't a problem.

I'm not disputing this answer, but I'm having a hard time seeing the difference in gust induced g-loading, and pilot (autopilot) induced g-loading. Having flown in intense weather aboard a plethora of varying acft, gust certainly can induce intense g-loads on planes...

@Jpe61 The difference is in the magnitude. Gusts feel intense, but it's their rapid changes in intensity that make it violent. The actual change in G-loading is smaller than what is possible in a turn.

So basically the old requirement of 50ft/s was just out of proportion with the load factor requirement, being too small? Still wondering how a rapidly changing loading is more demanding on the airframe than the same loading induced in a more controlled manner

@Jpe61 Loads create displacement. The skin bends around the rivets in one direction, then in the opposite one. A cyclic load of just a fraction of design strength can cause local low-cycle fatigue in high-stress areas. As for single high-jerk loads, they can shake loose non-structural parts; under gradually applied loads, they just settle.

Ok, got it now, makes perfect sense. Thanks

My question boils down to: how an aircraft can withstand very high momentary forces but not very high sustained forces.

From your question one can gather the maximum manuvering load factor has remained the same, and the turbulence intensity for design criteria has almost doubled.

How is it possible?

Fiber reinforced composites.
These materials can withstand repeated flexing far better than metals.
If one can imagine repeatedly bending a wooden stick and an aluminum tube, both may permanently deform under a similar stress load when broken "over the knee", but the wooden one may be more tolerant of repetitive bending without failing at a specific point due to fatigue.
It is this bending, "damping" or "shock absorption" superiority of more modern materials and building methods which may have lead to an increase in turbulence stress limits in design criteria, along with better understanding of weather phenomena such as microbursts.
One may also consider that a "transport" aircraft would not be designed for extreme manuvering, but would be required to fly in all weather.  Higher aspect, more flexible wings (as seen with the 787) would more likely be in the design.

Your answer seems to imply the design criteria for gust intensity was increased because materials have advanced. This is causally wrong, but I'm guessing it's not what you meant, so I would change the wording. Planes are still being built without fibre reinforced composites even though the design criteria is more demanding.

@Jpe61 the question is "how is it possible".  One could also step to another level structurally by adding materials or changing configuration.  The last paragraph seems to cover "why", feel free to edit in your input.

My point is that rules are changed to ensure safety, extremely rarely (no instances come to mind) because technology advances. Your "how is it possible" part would answer a question about "how is it possible that modern aircraft endure force X". The question here is about "how is it possible that rule Y changed, but a seemingly connected rule Z did not?"

@RobertDiGiovanni I'd concur that FRC are only one of many ways to improve turbulence resistance. Others include adhesives, welding, better riveting, better testing. All-metal aircraft comply with the same requirements. Other than the 787, the A350, and the MC-21, most currently-produced airliners are mostly metal.


text:
In big transport jets, what is the difference between manoeuvring loads and gust loads?
In the design certifications for big transport jets, there are two factors that must be met in order for a new aircraft to be certified; manoeuvring loads, and gust loads. Why are these two separate requirements, rather than simply specifying a minimum gravitational load factor?

Manoeuvring loads are well defined, controlled and regulated. The (auto-)pilot induces them, and the quasi-static loads can therefore be fully controlled.
Gust loads are sudden impulse loads, producing aeroelastic effects such as high speed buffet. Aero-elasticity, Mach number, wing sweep angle all play a role:

the faster the plane flies through the gust, the less affected it is;
the swept wing does not fly into the buffet all at once;
lower wing loading accelerates the aircraft with the gust earlier, and provides gust load relief;
torsion and bending stiffnesses of the wing must be such that no eigen-frequencies are induced from entering the gust.

The above is similar to what happens with a car during cornering on a smooth freeway, compared to driving at high speed over a bumpy surface.


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Does the center of mass for an airplane have to be over the wings?
I am designing a model aircraft that will have 4 propellers in a square configuration (think like a quadcopter) so that it can take off and move around like a quadcopter, then transition into plane flight like a VTOL aircraft.
For operating in quadcopter mode, it would be ideal for the center of mass to be in the center of the airframe (behind the main wing) for motor efficiency and agility reasons. If the CG is over the wing the front two motors will have to work harder than the back two, and while the PID controls will stabilize for this, it will decrease throttle headroom.

It depends on how much, and if your tail plane has enough down force to counter-act the natural tendency to pitch up. This can become a bigger problem in VTOL mode if the CoM is behind the rearmost propellers because the only thing left to make it pitch down is to run the front props in reverse... This is why aircraft like the Osprey have a very narrow CG margin.

No.
One relatively trivial example is a tandem wing (or a canard with a very large forward surface, if you will); the center of mass will be between the lifting surfaces, positioned so that the forward surface flies at a higher coefficient of lift than the rear (to give static longitudinal stability).
If you build your model with the motors on short arms, so that they're a bit above the wings when in quadcopter mode, you may be able to manage the CoM shift so that you automatically get the balance right for forward flight in wing lift.


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Are tracked landing gear systems still in use and development?
In the 1940's and 1950's, there were several tracked landing gear systems developed for the purpose of allowing landing on soft ground and/or using particularly heavy aircraft such as the B-36.
Are any such systems still in use and/or development?
(I have been searching and found quite a few examples but none in recent decades except for a proposal that suggests that it would be feasible to deploy modern improved tracked landing gear on C-130's, C-17's and 747s.)

The closest I can think of are skis for planes operating in the arctic/Antarctic. But those aren't tracks.

For the first half century of manned flight, landing gears overwhelmingly had only a single, large wheel per leg. This was the cheapest and simplest way to ensure ground mobility, but ran into trouble when aircraft grew in size. When the XB-36 prototype started testing in 1946, only three airfields in the US were able to tolerate the 156 psi pressure of its single main wheels.
For operating from unprepared surfaces, tracked gears were the straightforward transfer from tank experience to landing gear design.

Tracked main gear on the XB-36 prototype (picture source)
However, another route which was tried at about the same time was to increase the number of wheels the aircraft rests upon. With hindsight, the multi-wheel way was the better solution and has prevailed. When used with large, low-pressure tires it does not exert significantly more ground pressure than a tracked gear.
Some early and rather extreme examples for the multi-wheel route include the Arado 232 four-engine tactical transport aircraft. Only 20 were produced, however.

Arado 232 from up close. No prize for guessing why it had the nickname "Tausendfüssler" (millipede) (picture source).
When it comes to designing large aircraft for soft field operations, the Ukrainian design bureau Antonov has unsurpassed experience. This comes to bear in the landing gear of the Antonov 124, shown below (source). When you have 24 wheels to spread the load out, even 400 tons might not be too heavy, especially when the tire pressure can be adjusted from the cockpit.

An-124 in a botched landing. No worry, the gear will tolerate this kind of abuse, too.
Therefore, the research on tracked gears has come to an end shortly after it begun, and even the B-36 ended its days on a four-wheel bogie. Today, every large airplane has at least two wheels per leg for redundancy and sometimes a lot more.

This is a great answer for the very large aircraft. Do you know what has become of the technology for the scenarios for small aircraft on bad terrain which prompted the various small aircraft tracked landing gear systems developed in the 1940's and later?

@Dronz: As far as I know, tundra tires have won that race.

Magnesium Overcast, by Dennis R. Jenkins, is a history of the B-36, which covers the tracked landing gear experiments on pp.17-18. The XB-36 prototype was used for these experiments simply because it was a large and heavy aircraft that wasn't required for anything else at the time. One of his sources is an issue of the company's internal newsletter that's available online.
The problems with the tracked landing gear were that it added weight, about 5000lb for the XB-36, and that it made an unnerving screeching sound at high speed. Take-offs and landing were successful, but I suspect that it would have been substantially less durable than conventional undercarriage.
I doubt anyone is seriously considering the idea these days for large aircraft. Putting an unnecessary weight penalty on an aircraft is usually a poor idea, and making tactical landings in very large and heavy aircraft exposes that valuable asset to the enemy. It makes more sense to use tactical aircraft for tactical jobs.

Thanks. Your reasoning is about huge systems, though, and there are several early examples of tracked landing gear which were on small aircraft (e.g. see the article at the first link in my question). 2) The one modern mention of tracked landing gear I did find was considering using them (and with large aircraft)  though the presentation was not well edited and I'm not clear where it comes from. It expected there to be technological improvements available, but I didn't see a reference to them actually having been developed.


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What causes a normal shock wave on a wing?
I am wondering what causes a normal shockwave on a wing? I mean why does the airflow (that becomes supersonic over a part of the airfoil) slows down somewhere over that wing suddenly to a subsonic speed (what probably causes a shock).

The slowdown process occurs at the shock surface. The air entering the shock surface from upstream is supersonic and the air exiting the shock surface downstream is subsonic. The thickness of the shock zone is quite small compared to the chord of the wing.
Sonic shock waves occur because in order for air to get out of the way of something traveling through it, that something has to be moving more slowly than the air's ability to communicate to other parcels of air that "something's on the way". That communication speed is the speed of sound. If the object is moving faster than that, then the air it is running into has no advance warning and cannot start getting out of the way before the object arrives. The result is a shock wave.
The physics of shock waves is well-described on-line.